The present invention relates to a motor to be used for recording and/or reproducing information stored in a compact disc or a video disc, and an apparatus using the same motor. More particularly, it relates to a motor structure which can improve oil-holding performance of oil-impregnated metal, and a motor structure which can restrain a rotor from moving and vibrating axially due to axial attraction from an attracting magnet.
Recently, oil-impregnated metal made of porous metal has been widely used for a bearing in order to meet a requirement of lowering cost of motors that drive optical discs or optical-magneto discs for recording and/or reproducing information stored therein. However, an apparatus such as a compact-disc player or a videodisc player runs at a speed higher than ever, and this trend reduces long-term reliability of the bearing, and thus the motors encounter the following problems:
necessity of an oil-holding structure of the oil-impregnated metal which forms the bearing; and
measures against oil splashing from the oil-impregnated metal.
If a rotor moves or vibrates axially when the motor is driven at a high speed, errors could occur in reading/writing information from/to a disc.
A conventional motor is disclosed in Japanese Published Unexamined Patent Application No. H08-289523. FIG. 9 shows a construction of conventional motor. In FIG. 9, shaft 101 transmits rotation. Ring-shaped rotor-magnet 103 is press-fitted or rigidly bonded to an inner wall of frame 102. Magnet 103 is multipolar magnetized in a circumferential direction. A burring process is applied to a central section of frame 102, and shaft 101 is directly press-fitted into the burring-processed section. Rotor 111 comprises shaft 101, frame 102 and magnet 103.
Bracket 104 made of magnetic material is formed by press working, and has a burring-processed section 112 that projects like steps at an approximately central portion thereof. Burring-processed section 112 works as bearing housing 123 accommodating a bearing. Bracket 104 includes burring-processed section 112 with which mounting-base 113 is unitarily formed. Mounting-base 113 is used for mounting a motor to an apparatus.
On an inner wall of burring-processed section 112, oil-impregnated metal 105 is press-fitted for supporting shaft 101 rotatably. On the other hand, on an outer wall of burring-processed section 112, stator core 114 is press-fitted. On stator core 114, copper wire 106 is wound via an insulator made of resin.
Printed circuit board 107, which includes at least a part of circuits driving and controlling the motor, is rigidly bonded to mounting-base 113 with double-faced adhesive tape (not shown). An end of copper wire 106 is connected onto board 107.
Stopper 108, for preventing rotor 111 from coming off in a thrust direction, is formed by metal pressing work. Stopper 108 is press-fitted onto an end of shaft 101. Bottom plate 109 bears load of rotor 111 in the thrust direction via resin board 110 exhibiting abrasion resistance. Bottom plate 109 is press-fitted into an inner wall of burring-processed section 112.
A plurality of through-holes 116 are punched in a top plate of frame 102. When bottom plate 109 is press-fitted into section 112, face xe2x80x9cPxe2x80x9d of stator core 114 can be supported with a jig (not shown) extending through holes 116, so that a force caused by press-fitting is restrained from being applied to mounting-base 113.
However, the structure discussed above allows oil leaked from a top of oil-impregnated metal 105 to splash outwardly during rotation of rotor 111. The oil splashed moves to stator core 114, travels on the inner wall of frame 102 and arrives at magnet 103.
As a result, the oil impregnated in metal 105 decreases, which lowers reliability of the bearing spinning at a high speed. Thus, the motor is not suited for an apparatus demanded to spin at a higher speed.
In the conventional motor discussed above, attraction force (called magnetic thrust) working axially between stator 115 and rotor 111 is produced by deviation between a center of an axial length of stator core 114 and a center of an axial length of rotor magnet 103. In other words, the attraction force can be produced by shifting magnetic center H1 appropriately. This attraction force working between stator 115 and rotor 111 allows a disc to vibrate less in an axial direction, thereby preventing read/write errors.
Another conventional motor, having different structure to produce an attraction force, is disclosed in Japanese Published Unexamined Patent Application No. H11-55900. The motor disclosed in this application comprises the following elements:
a rotary shaft;
a bearing for journaling the rotary shaft;
a hub fixed to the rotary shaft;
a stopper, for preventing a motor from coming off, made of magnetic material and fixed to the hub;
an attracting magnet mounted to the stopper;
a bracket for holding the bearing; and
a coil assembly fixed to the bracket.
The attracting magnet faces a core of the coil assembly. The stopper slides with the bearing only when a rotating body moves. This structure prevents the motor from coming off, and restrains vibrations in both a radial and a thrust direction.
However, according to the publication discussed above, oil leaked from an oilless bearing cannot be collected or returned to the bearing per se; therefore, it is difficult to further improve reliability of the motor spinning at a higher speed. Major magnetic field produced by a driving current running through the coil is affected by magnetic flux from the attracting magnet because the attracting magnet is disposed closely to the coil assembly, and the major magnetic field produces magnetic interference.
Still another conventional motor is disclosed in Japanese Published Unexamined Patent Application No. 2000-245116. This conventional motor comprises the following elements:
a stationary member;
a rotor rotatable with respect to the stationary member;
a bearing disposed between the stationary member and the rotor;
a rotor magnet mounted to the rotor; and
a stator mounted to the stationary member.
The rotor includes a cup-shaped rotor made of magnetic material. The cup-shaped rotor has an annular wall and an end wall disposed on a first end of the annular wall. The rotor magnet is formed of a sheet-like rubber magnet. This rubber magnet is mounted forming a ring shape on an inner face of the annular wall. Magnetic energizing structure, for energizing the rotor axially, is mounted to the stationary member, wherein the magnetic energizing structure includes a sintered magnet of ferrite system and faces the end wall of the cup-shaped rotor. This structure allows the conventional motor to be manufactured at a lower cost and obtain desirable energizing force.
However, this structure needs additionally a holder as an element of the magnetic energizing structure, and yet, this structure cannot collect oil leaked from an oilless bearing or return the oil to the bearing per se. Therefore, it is difficult for this structure to further improve reliability of the bearing spinning at a higher speed. Furthermore, since the energizing structure is placed above the stator core, this structure is not suited for a motor used in a slim apparatus.
The present invention addresses the problems discussed above, and aims to provide a motor suitable for a disc driving apparatus which records and/or reproduces information stored in a compact disc, videodisc, optical disc, optical magneto disc or the like, and an apparatus using the same motor.
To be more specific, the present invention aims to provide a motor structure that meets a requirement of downsizing and lowering of profile of an apparatus as well as improves reliability of a motor-bearing spinning at a higher speed. At the same time, the present invention aims to provide a motor in a simple construction which prevents a disc from moving or vibrating in an axial direction in order to reduce read/write errors, and an apparatus using the same motor.
The motor of the present invention comprises the following elements:
(a) a bracket incorporating a bearing housing, and a mounting base for mounting a motor to an apparatus;
(b) oil-impregnated metal fixed to an inner wall of the bearing housing;
(c) a stator in which a stator core wound with coils is disposed on an outer wall of the bearing housing;
(d) a rotor including a frame having a plurality of through holes in a top surface of the frame, a shaft fixed to the frame, and a rotor magnet fixed to the frame; and
(e) a cap facing the through holes and disposed at a place spaced from the through holes.
The apparatus of the present invention includes a housing, and the motor discussed above is mounted in the housing via the mounting base.
The motor structure discussed above allows the stator to be supported with, e.g., supporting-pins through the through holes because the cap is positioned at a place corresponding to the through holes punched in the frame. Force generated in assembling the motor is thus not applied to the mounting base, so that the assembly does not impair precision of the mounting base. Further, the cap can prevent oil from splashing.